I have noticed that if I make a manual brim that is at layer height (0.2mm) then I get almost no warping when printing PLA on a "cold" bed. However I do get some (not terrible) warping with a slic3r brim (8mm around a 40mm diameter circular footprint)
I was curious if anyone had actual evidence (as opposed to hunches and feelings!) as to what is more important in this particular scenario is it the thermal mass (in effect the brims "heat inertia" or hopefully lack thereof) or the physical weight of the brim, that is important, or maybe they are both as important?
Of course the big drawback of a manual brim is although you can cut it with scissors easily and tear it along the "grain" you still have to spend time with a file to tidy the model where as the auto brim almost tears off without too much difficulty...
